Recycling of metals and metal alloys is becoming increasingly important to maintain global environmental quality. Aluminum cans and other containers, for example, are recycled at higher levels than a decade ago. Currently, over 50% of all aluminum cans (also referred to as “Used Beverage Containers” or “UBC's”) in the United States are recycled.
Current alloy chemistries in aluminum cans, however, create a metallurgical limit on the relative percentage of aluminum feedstock that can be derived from UBC's. Two common alloys for aluminum cans, by way of illustration, are AA 3004 (which is used for body stock) and 5182 (which is used for end and tab stock). AA 3004 commonly includes 0.8 to 1.3 wt. % magnesium and 0.9 to 1.5 wt. % manganese, while AA 5182 commonly includes from 4.0 to 5.0 wt. % magnesium and from 0.20 to 0.50 wt. % and more commonly no more than 0.35 wt. % manganese. AA 3104, another useful alloy for body stock, commonly includes 0.8 to 1.3 wt. % magnesium and 0.8 to 1.4 wt. % manganese. Assuming that body stock constitutes about 72 wt. % of the UBC while end and tab stock constitute about 28% of the UBC, a melt formed from a UBC currently contains about 1.71 wt. % magnesium and about 0.75 wt. % manganese. To form body stock from the UBC, the magnesium level needs to be reduced to about 1 wt. %. This reduction is effected using prime aluminum feedstock, thereby placing a practical limit of about 55 to 60 wt. % on the amount of aluminum feedstock that can be derived from UBCs.
A higher percentage of magnesium in the feedstock can cause problems in can manufacture. While the magnesium level in a UBC melt, which typically varies between 1.3 to 1.6 wt. %, is below the magnesium level in the AA 5182 alloy, which is specified as being between 4 and 5 wt. %, it is above the magnesium level in the AA 3004 and AA 3104 alloys, which is specified as being between 0.8 to 1.3 wt. %. Magnesium is a much more effective hot or cold work hardener compared to manganese. Higher magnesium levels in body stock can increase tear offs in the body maker and lead to problems in fabricating the neck and flange. By contrast, higher manganese levels than those specified for AA 5182 alloy (which varies between 0.20 to 0.50 wt. %) can be tolerated in the manufacture of ends from end stock.
There is a need for a container alloy composition and method of manufacture that can provide higher levels of UBC recycle.